- Email: [email protected]
Direct pulp capping of permanent teeth in primates using a resorbable form of tricalcium phosphate ceramic
JOURNAL OF ENDODONTICS i VOL. 1, NO. 3, MARCH 1975
Direct pulp c a p p i n g of p e r m a n e n t teeth in p r i m a t e s u s i n g a r e s o r b a b l e f o r m of t r i c a l c i u m p h o s p h a t e c e r a m i c Alfred L. Heller, DDS, MS; Cdr Joseph F. Koeniqs (DC) USN; J. David Brilliant, DDS, MS; Rudy C. Melfi, DDS, PhD; and Thomas D. Driskell, BS, Columbus, Ohio
A r e s o r b a b l e c e r a m i c w a s p l a c e d o v e r 22 s u r g i c a l l y c r e a t e d p u l p a l e x p o s u r e s in a n e x p e r i m e n t . H i s t o l o g i c a l e v i d e n c e s h o w e d that f o r m a t i o n of a d e n t i n a l b r i d g e took p l a c e b y d i r e c t a p p o s i t i o n on the p u l p a l t i s s u e s that w e r e t r e a t e d w i t h a c e r a m i c form of t r i c a l c i u m p h o s p h a t e . F o r m a t i o n of a d e n t i n a l b r i d g e a p p e a r s to b e p r e d i c t a b l e . T h e b r i d g e is c o n t i g u o u s a n d thick, p u l p a l i n f l a m m a t i o n is m i n i m a l , a n d o d o n t o b l a s t s a r e o b s e r v e d d i r e c t l y u n d e r a n d in c o n t a c t w i t h the b r i d g e . The c e r a m i c form of t r i c a l c i u m p h o s p h a t e a p p e a r s to e n h a n c e the f o r m a t i o n of a d e n t i n a l b r i d g e in c o n t r a s t with the c a l c i u m h y d r o x i d e that w a s u s e d a s the control.
Stanley ~ said that about 250,000 teeth are extracted each day in the United States. There is a great need for a more effective pulp-capping material that would enable an increased number of these teeth to survive without the use of elaborate procedures. The clinician's goal is the formation of a dentinal bridge over the site of exposure and the maintenance of a vital pulp. It is even more important that the dentinal bridge is capable of protecting the delicate tissue of the pulp. Calcium hydroxide and a mixture of zinc oxide and eugenol are the two materials most often used in the pulpcapping treatment of permanent teeth. Berman and Massler 2 reported no
basic clinical difference between calcium hydroxide and a mixture of zinc oxide and eugenol as pulp-capping materials. However, histologic studies by Glass and Zander, 3 Doyle and associates, 4 and Nyborg 5 demonstrated that although the pulp may remain vital when capped with zinc oxide and eugenol, a chronic inflammatory reaction persists subjacent to the area of the exposure, whereas calcium hydroxide appears to stimulate the mesenchymal cells to lay down a bridge of dentoid. Langeland 6 said that current pulpcapping agents are not useful; he recommended root canal therapy when the pulp is exposed. He felt that a bridge induced by calcium hydroxide
has many soft tissue inclusions; when viewed in serial histological sections, it has a "swiss cheese" appearance rather than an appearance of a solid bridge. Bhaskar and associates 7 reported the use of a resorbable ceramic implanting material (tricalcium phosphate) in the bone tissue of rats as noninflammatory, resorbable, and osteogenic. The tricalcium phosphate ceramic was phagocytized by the mesenchymal cells; this can be seen within their cytoplasm by electron photomicrography. DriskelI s said that the porous tricalcium phosphate ceramic most nearly approximates the ratio of calcium and phosphorus in the hydroxyapatite mineral phase found in natural bone. The purpose of this study was to evaluate tricalcium phosphate ceramic powder as a direct pulp-capping agent on the permanent teeth of monkeys. This agent is a physiologically resorbable ceramic material with a particle size of 149 micrometers (/xm) or less.
Materials a n d Methods Twenty-nine
teeth in four adult
Cynalmolgus monkeys were used in
95
JOURNAL OF ENDODONTICS
the experiment. Radiographs were taken before and after each pulp-capping procedure. Molars and premolars were selected because of their larger pulpal chambers. Maxillary right first molars and premolars were used as control teeth with calcium hydroxide. Tricalcium phosphate ceramic powder* was used in the remaining molars and premolars. All animals were approximately four years of age and were close to the same weight. The anesthetics used were phencyclidine hydrochloride intramuscularly and pentobarbital intravenously. Atropine was administered intramuscularly to control salivation. The teeth were isolated with a rubber dam. They were disinfected with povidone-iodine solution for five minutes. The occlusal portion of the tooth was opened with a high-speed no. 4 round bur. The same bur was used to remove the roof of the pulpal chamber. The vital pulpal tissue in the chamber was removed with a small-spoon excavator to minimize injury to the remaining tissue in the root canals. After the pulpotomy was completed, hemorrhage was controlled with a sterile cotton pellet. Pressure was applied until a blood clot formed on the canal tissue stumps. The excess blood and the clot were rinsed from the chamber with physiological saline solution. A paste of tricalcium phosphate ceramic powder in physiological saline solution was applied to 22 teeth as the experimental pulp-capping material. A paste of calcium hydroxide powder in physiological saline solution was applied to the pulp stumps of seven teeth as the control material. The pulp-capping materials were placed over the blood clot of the pulpal tissue of the canals. Because of the evaporation of the saline solution, it was difficult to place the same amount of paste over each site of exposure. After the calcium hydroxide or tri96
calcium phosphate ceramic paste was placed as the pulp-capping agent, a mix of fast-setting zinc oxide and eugenol was used to form a protective base before placement of the final amalgam restoration. The zinc oxide and eugenol base was placed with care to avoid pushing the pulp-capping materials into the tissue of the canal. Radiographs were taken preoperatively, postoperatively, and immediately postmortem. The monkeys were anesthetized with phencyclidine hydrochloride and pentobarbital; they were killed by perfusion with 10% Formalin at 2-, 3-, 5-, 8-, 16-, and 24-week periods. After death, the mandible and maxilla were removed and stripped of soft tissue; they were sectioned so that a tooth remained in each section. The block sections were fixed in 10% Formalin for two weeks and then demineralized in 5% formic acid. The specimens then were embedded in paraffin and cut serially at 6/xm to 10/zm. Each section was cut longitudinally in a mesiodistal plane. Every fifth section was stained routinely with hematoxylin and eosin and examined microscopically. In areas that were important to the study, every section was stained. The results were evaluated in the following manner: The pulps were examined for low, moderate, or severe inflammation, and for vascularization. Connective tissue repair of the pulp at the site of exposure; calcification of the site of exposure; and the conditions of the odontoblastic and predentinaI layers and the periapical tissue were evaluated. Results
No gingival disease was observed before the initiation of the operative procedures or just before killing. The radiographs that were taken before the pulp-capping procedures, immediately after the procedures, and at the
VOL. 1, NO. 3, MARCH 1975
time of killing showed no periapical changes. Because of the small pulpal canals, the presence or absence of a calcified bridge could not be discerned radiographically, either with the ceramic form of tricalcium phosphate or calcium hydroxide. The following results are histological evidence of the specimens. 9 Two-week postoperative experimental results. Three specimens were examined (Fig 1, top). The specimens showed evidence of a fibrous matrix forming at the coronal end of the root canal. There was no evidence of a calcified bridge. There was a characteristic compartmentalization of this matrix. These compartments appeared to be areas of connective tissue surrounding the tricalcium phosphate ceramic particles; there was evidence of a generous blood supply. The compartments gave the appearance of a basket-weave; the connective tissue and tricalcium phosphate ceramic particles were interspersed throughout the coronal portion of the canal. The index of inflammation was low. The odontoblasts appeared viable and undisturbed while the predentinal layer was thickened. The periapical tissues s h o w e d n o evidence of inflammation. 9 Two-week postoperative control. Two specimens were examined (Fig 1, bottom). One specimen showed complete necrosis throughout the pulpal chamber; the canals had moderate periapical inflammation. The other specimen showed evidence of a fibrous matrix beginning to develop at the coronal end of the root canals. A low index of inflammation was evident in the coronal portion of the pulpal canals. There was no inflammation in the periapical tissues. The odontoblasts appeared undisturbed with no thickening of the predentinal layer. 9 Three-week postoperative experimental results. Three specimens were examined (Fig 2, left). Each speci-
JOURNAL OF ENDODONTICS [ VOL. 1, NO. 3, MARCH 1975
Fig 1--Top: Two-week postoperative experimental results (FM, fibrous matrix; TCPC, tricalcium phosphate compartments; BS, blood supply). Dark areas are tricalcium phosphate ceramic particles. Bottom: Two-week postoperative control (D, dentin; O, odontobIasts (orig mag XIO0)).
Fig 3--Top left: Five-week postoperative experimental results (TCPC, tricalcium phosphate compartments; BS, blood supply; CM, calci/ied matrix; O, odontoblasts). Bottom: Five-week postoperative experimental results (TP, thickened predentin). Top right: Five-week postoperative control. Void areas are seen in pulpal tissue adjacent to calcified bridge and thickened predentin (orig mag XIO0). men showed similar results when compared to the two-week specimen except for the evidence of a more developed matrix forming over the exposed pulp. A low index of inflammation was observed in both the coronal and apical portions of the pulp; there was no inflammation in the periapical tissues. There was evidence of a thickened predentinal layer continuous with the fibrous matrix. Vascular supply was evident throughout the pulpal tissues. The odontoblasts were undisturbed.
9 Three-week postoperative control. Fig 2--Left: Three-week postoperative experimental results (FM, fibrous matrix; TCPC, tricaIcium phosphate compartments; BS, blood supply). Right: Three-week postoperative control (Abs, abscess; V, vacuoles seen throughout odontoblastic layer (orig mag XIO0)).
The specimen that was examined (Fig 2, right) showed a fibrous matrix forming at the coronal end of the root canals. There was a large void area lined with connective tissue that 97
JOURNAT. OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
Fig 5--Le/t: Sixteen-week postoperative experimental results. Dark granules are remaining tricalcium phosphate particles (TCPC, tricalcium phosphate compartments; CM, calcified matrix; TP, thickened predentin; BS, blood supply). Right: Sixteen-week postoperative control (CB, calcified bridge; D, dentin; O, odontoblasts (orig mag X250)).
Fig 4--Top: Eight-week postoperative experimental results (TCPC, tricalcium phosphate compartments; CM, calcified matrix; V, viable cells in matrix; O, odontoblasts; BS, blood supply). Bottom: Eight-week postoperative control (CB, calcified bridge; D, dentin; R, reticular atrophy; Abs, abscess (orig mag XIO0)).
was apical to the forming matrix. There were vacuoles throughout the odontoblastic layer and moderate inflammation adjacent to the forming matrix. The predentinal layer was thickened. There was a low index of inflammation in the periapical tissues.
9 Five-week postoperative experimental results. In the four specimens that were examined (Fig 3, top left, bottom), there was evidence of a cal98
cified matrix forming at the coronal end of the root canals. The compartments were well-defined; the walls surrounding the remaining tricalcium phosphate ceramic were thicker than was evident in the three-week study. It appeared that the tricalcium'phosphate ceramic particles were being phagocytized or were being dissolved within the matrix compartments. All four specimens showed viable odontoblasts with a thickened predentinal layer continuous with the calcified matrix. Some areas of the predentinal layer contained cells that appeared to be entrapped odontoblasts. The thickened predentinal layer and calcified matrix formed a continuous cap over the exposed pulp. Histological serial sections showed that the calcified matrix Was a complete layer from one side of the canal to the other. Blood vessels were evident throughout the compartmentalized matrix. The periapical tissues and the apical pulpal tissues were free of inflammation.
9 Five-week
postoperative
control.
The specimen that was examined (Fig 3, top right) showed a well-developed bridge. Histological serial examination showed that the bridge was not complete from wall to wall of the canal.
The predentinal layer was thickened and continuous with the calcified bridge. There were few odontoblasts adjacent to the coronal portion of the bridge. There was evidence of a void area beginning adjacent to the thickened predentinal layer and inferior to the calcified bridge. Apical odontoblasts a~apeared to be viable with a small amount of predentinal thickening. There were few blood vessels. The periapical tissue and the apical pulpal tissue showed a low index of inflammation.
9 Eight-week postoperative experimental results. Three specimens were examined (Fig 4, top). The individual compartments showed more calcification than the five-week specimens did; there was less evidence of particles of tricalcium phosphate ceramic. Viable cells, perhaps fibroblasts or ostoidproducing cells, were evident within the areas of the matrix. The odontoblastic layer was viable and undisturbed from the coronal matrix to the apex. The predentinal layer was thickened only at the coronal portion
JOURNAL OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
where it united with the calcifying matrix. The pulpal tissues showed no inflammation; they had an abundant blood supply. Histological serial sections showed that the calcified matrix was complete from one side of t h e canal to the other in two specimens. In the other specimen, it was almost complete. The periapical tissues showed no inflammation.
9 Eight-week postoperative control. The specimen that was examined (Fig 4, bottom) showed a calcified bridge. Serial sections showed that the calcified bridge was not complete from one side of the canal to the other side; there was soft tissue in some sections. The odontoblastic layer showed areas of vacuolization from the calcified bridge to the apex. There was no evidence of thickening of the predentinal layer below the bridge. Reticular atrophy with areas of scattered necrosis was observed in the center of the pulpal tissue. An abscess appeared to be forming under an area of the bridge in several sections. There were few blood vessels. The pulpal and periapical tissues had a low index of inflammation.
9 Sixteen-week postoperative experimental results. Of the three specimens that were examined (Fig 5, left), one specimen showed complete necrosis throughout the chamber and canal. The periapical tissue had a low index of inflammation. The other two specimens Fig 5, left showed the characteristic compartmentalization of the calcified matrix. Most of the particles of tricalcium phosphate ceramic had resorbed within the compartments; this allowed for thicker and more calcified walls. The predentinal layer was thickened and contiguous with the calcifying matrix. Serial sections showed that the calcified matrix formed a complete wall-to-wall bridge of the canals. Viable cells were evident within the calcifying matrix. The pulpal tissues and periapical tissues showed no inflammation. The odontoblasts
Fig 6--Twenty-/our week postoperative experimental results. Top le/t: CM, calcified matrix; CB, calci/ied bridge; D, dentin (orig mag XIO0). Bottom: O, odontoblasts; TP, thickened predentin (orig mag X250). Top right: (orig mag X250). were not well defined. Blood vessels were throughout the pulpal tissue as well as within the compartmentalized matrix.
9 Sixteen-week postoperative control. One specimen was examined (Fig 5, right). Serial sections showed that a calcified bridge was formed that was completely wall to wall of the canal. The pulpal and periapical tissues showed no evidence of inflammation. The dentinal walls of the pulpal canals were irregular. The predentinal layer was thickened at the coronal end of the pulpal canals while the odontoblasts were undisturbed. Blood vessels were observed throughout the pulpal tissue.
9 Twenty-/our week postoperative experimental results. Three specimens were examined (Fig 6); they showed essentially the same results. The most coronal portion of the pulpal cap
showed very little evidence of remaining tricalcium phosphate ceramic. The walls of the calcified matrix were thicker than the walls of the 16-week specimen; thus, the individual compartments were smaller. Cells were evident within the walls of the calcified matrix. There were blood vessels throughout the calcified matrix and compartments. Directly under the calcified matrix compartments, there was an area of scattered solid calcifications mixed with blood vessels. Apically, there was an area of complete calcification. Serial sections showed a complete wall-to-wall bridge of the canals. The bridge showed evidence of a few cells. U n d e r the calcified bridge, there was an area of thickened predentin that was contiguous with the thickened predentinal area from the sides of the canal walls. The thickened portion of predentin was corn-
99
JOURNAL OF ENDODONTICS [ VOL. 1, NO. 3, MARCH 1975
plete throughout from one side to the other side of the canals. Directly under the predentinal layer, there was a continuous line of odontoblasts in direct apposition to the predentinal layer adjacent to the calcified bridge. The odontoblasts were viable and functional as shown by the thickness of predentin. A few small calcified bodies were in apposition to the coronal odontoblasts. Both the pulpal and periapical tissues were vascular; there was no evidence of inflammation.
9 Twenty-four week postoperative control. The specimen that was examined (Fig 7) showed complete necrosis of the pulpal chamber and the pulpal canal. There was evidence of moderate inflammation of the periapical tissue and possible formation of an abscess in the periapical tissues.
Discussion The results of the study showed that the ceramic form of tricalcium phosphate stimulates the formation of a calcified bridge and that it maintains
Fig 7--Twenty-four week postoperative control (I), dentin; NCP, necrotic pulpal canal (orig mag X58)).
100
a noninflammatory, viable pulp. Twenty-one of 22 pulps treated with tricalcium phosphate ceramic showed favorable results histologically. Three reasons are possibly responsible for this result. The first reason is the development and close apposition of a blood supply to the calcified bridge. The second reason is a possible anti-inflammatory capability in this material. The third reason may be the close chemical resemblance of tricalcium phosphate ceramic to bone or dentin or both. The breakdown products of the tricalcium phosphate may possibly be a contributory factor toward development of the calcified bridge. Both Nyborg '~ and Clark I o showed that there was an area of necrosis and lysed red blood cells adjacent to the calcified bridge when calcium hydroxide was used. Therefore, the calcium hydroxide actually causes the necrosis; this stimulates the pulpal cells to lay down a calcified bridge. However, this bridge usually does not have a vascular supply. This study confirmed their findings. It is likely that some of the zinc oxide and eugenol cement was unavoidably pushed through the layers of calcium hydroxide and tricalcium phosphate ceramic paste; this could have affected the results. Only 1 of 22 pulps reacted unfavorably histologically when treated with tricalcium phosphate ceramic. However, after the same procedures with calcium hydroxide, two teeth had completely necrotic pulps and one tooth had a partial bridge with an underlying pulpal abscess and reticular atrophy. Thus, calcium hydroxide histologically failed three of seven times as a direct pulp-capping agent. In the other four teeth, the pulps remained viable; two formed a fibrous protective matrix, one formed a partial bridge, and one formed a completely calcified bridge.
This study was conducted with the use of healthy teeth of adult monkeys. Further studies are needed using teeth whose pulps have been exposed because of caries or trauma. Further studies also are needed to find a cement-type base material that is potentially less toxic to pulpal tissue than zinc oxide and eugenol. Polycarboxylate cement holds promise as a cement-type base material. 11 Tricalcium phosphate ceramic should be studied for periods of longer time to evaluate the healed pulp's reaction to the test of time and also its response to new insult. There is also the question: If endodontic therapy is ultimately necessary, would there be interfering aberrant calcifications that would complicate treatment? Tricalcium phosphate ceramic appears to be an excellent pulp-capping material; it is inexpensive and easily applied. Clinical studies of human teeth are now felt to be desirable to substantiate the findings of the study.
Summary The purpose of the study was to evaluate a resorbable form of tricalcium phosphate ceramic as a direct pulp-capping agent in the permanent teeth of monkeys. Tricalcium phosphate ceramic powder was mixed with physiological saline solution and was used as a direct pulpal cap in 22 teeth. As a control, the pulps of seven teeth were capped with calcium hydroxide powder mixed with physiological saline solution. The monkeys were killed at 2-, 3-, 5-, 8-, 16-, and 24-week intervals. One of the 22 teeth whose pulp was capped with tricalcium phosphate ceramic showed a necrotic pulp. The remaining teeth showed various levels of formation of matrix, vascularization, and compartmentalization. The 24week specimens showed contiguous calcified bridges spanning the sites of exposure.
JOURNAL OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
Of the seven teeth whose pulps were capped with calcium hydroxide, two showed completely necrotic pulps, and one showed a partially calcified bridge with a pulpal abscess and reticular atrophy. In the other four teeth, the pulps remained viable; two formed a fibrous protective matrix, one formed a partial bridge, and one formed a completely calcified bridge. Conclusions
A contiguous calcified bridge can be expected to form over a pulpal exposure when it is capped with tricalcium phosphate ceramic. The pulpal tissue was in close apposition to the calcified bridge and showed minimal inflammation; the pulpal tissue was well vascularized. An odontoblastic layer lined the pulpal surface of the calcified bridge. A thickened layer of predentin lined the walls of the canal and was contiguous with the calcified bridge. Tricalcium phosphate ceramic should be used experimentally as a direct pulp-capping agent in studies on human teeth.
*Synthos: A high purity, specially prepared and processed form of tricalcium phosphate. MITER, Inc., 633 High St, Worthington, Ohio 43085. The opinions and assertions herein are those of the authors and are not to be construed as official or as reflecting the views of the Navy Department or the naval service at large. Dr. Heller is an endodontist in private practice; Dr. Koenigs is an active duty endodontist (DC) USN; Dr. Brilliant is director of graduate endodontics, Ohio State University School of Dentistry; Dr. Melfi is chairman of biological studies, Ohio State University School of Dentistry; and Mr. Driskell is an adjunct professor, Ohio State University School of Dentistry. Requests for reprints should be directed to Dr. Heller, 6586 Worthington-Galena Road, Worthington, Ohio 43085.
References
1. Stanley, H.R. How much could we learn? Justification for establishing a registry for pulpal pathology. Oral Surg 29:265 Feb 1970.
2. Berman, D.S., and Massler, M. Experimental pulpotomies in rat molars. J Dent Res 37:229 April 1958. 3. Glass, R.L., and Zander, H.A. Pulpal healing. J Dent Res 28:97 April 1949. 4. Doyle, W.A.; McDonald, R.E.; and Mitchell, D.F. Formocresol versus calcium hydroxide in pulpotomy. J Dent Child 29:86 April-June 1962. 5. Nyborg, H. Capping of the pulp. The processes involved and their outcome. A report of the follow-ups of a clinical series. Odontol Tskr 66:296, 1958. 6. Langeland, K. Capping exposed pulpal tissue. Clin Dent 2:1 Jan-Feb 1974. 7. Bhaskar, S.N., and others. Biodegradable ceramic implants in bone. Electron and light microscopic analysis. Oral Surg 32:336 Aug 1971. 8. Driskell, T.D., and others. The significance of resorbable bioceramics in the repair of bone defects. Proc 26 Annual Conference on Engineering in Medicine and Biology. 1973. 9. Nyborg, H. Healing processes in the pulp on capping. Acta Odontol Scand 13:9 (Suppl. 16) 1955. 10. Clarke, N.G. The morphology of the reparative dentine bridge. Oral Surg 29:746 May 1970. 11. Spangberg, L.; Rodrigures, H.; and Langeland, K. Biologic effects of dental materials. Oral Surg 37:113 Jan 1974.
101
Direct pulp c a p p i n g of p e r m a n e n t teeth in p r i m a t e s u s i n g a r e s o r b a b l e f o r m of t r i c a l c i u m p h o s p h a t e c e r a m i c Alfred L. Heller, DDS, MS; Cdr Joseph F. Koeniqs (DC) USN; J. David Brilliant, DDS, MS; Rudy C. Melfi, DDS, PhD; and Thomas D. Driskell, BS, Columbus, Ohio
A r e s o r b a b l e c e r a m i c w a s p l a c e d o v e r 22 s u r g i c a l l y c r e a t e d p u l p a l e x p o s u r e s in a n e x p e r i m e n t . H i s t o l o g i c a l e v i d e n c e s h o w e d that f o r m a t i o n of a d e n t i n a l b r i d g e took p l a c e b y d i r e c t a p p o s i t i o n on the p u l p a l t i s s u e s that w e r e t r e a t e d w i t h a c e r a m i c form of t r i c a l c i u m p h o s p h a t e . F o r m a t i o n of a d e n t i n a l b r i d g e a p p e a r s to b e p r e d i c t a b l e . T h e b r i d g e is c o n t i g u o u s a n d thick, p u l p a l i n f l a m m a t i o n is m i n i m a l , a n d o d o n t o b l a s t s a r e o b s e r v e d d i r e c t l y u n d e r a n d in c o n t a c t w i t h the b r i d g e . The c e r a m i c form of t r i c a l c i u m p h o s p h a t e a p p e a r s to e n h a n c e the f o r m a t i o n of a d e n t i n a l b r i d g e in c o n t r a s t with the c a l c i u m h y d r o x i d e that w a s u s e d a s the control.
Stanley ~ said that about 250,000 teeth are extracted each day in the United States. There is a great need for a more effective pulp-capping material that would enable an increased number of these teeth to survive without the use of elaborate procedures. The clinician's goal is the formation of a dentinal bridge over the site of exposure and the maintenance of a vital pulp. It is even more important that the dentinal bridge is capable of protecting the delicate tissue of the pulp. Calcium hydroxide and a mixture of zinc oxide and eugenol are the two materials most often used in the pulpcapping treatment of permanent teeth. Berman and Massler 2 reported no
basic clinical difference between calcium hydroxide and a mixture of zinc oxide and eugenol as pulp-capping materials. However, histologic studies by Glass and Zander, 3 Doyle and associates, 4 and Nyborg 5 demonstrated that although the pulp may remain vital when capped with zinc oxide and eugenol, a chronic inflammatory reaction persists subjacent to the area of the exposure, whereas calcium hydroxide appears to stimulate the mesenchymal cells to lay down a bridge of dentoid. Langeland 6 said that current pulpcapping agents are not useful; he recommended root canal therapy when the pulp is exposed. He felt that a bridge induced by calcium hydroxide
has many soft tissue inclusions; when viewed in serial histological sections, it has a "swiss cheese" appearance rather than an appearance of a solid bridge. Bhaskar and associates 7 reported the use of a resorbable ceramic implanting material (tricalcium phosphate) in the bone tissue of rats as noninflammatory, resorbable, and osteogenic. The tricalcium phosphate ceramic was phagocytized by the mesenchymal cells; this can be seen within their cytoplasm by electron photomicrography. DriskelI s said that the porous tricalcium phosphate ceramic most nearly approximates the ratio of calcium and phosphorus in the hydroxyapatite mineral phase found in natural bone. The purpose of this study was to evaluate tricalcium phosphate ceramic powder as a direct pulp-capping agent on the permanent teeth of monkeys. This agent is a physiologically resorbable ceramic material with a particle size of 149 micrometers (/xm) or less.
Materials a n d Methods Twenty-nine
teeth in four adult
Cynalmolgus monkeys were used in
95
JOURNAL OF ENDODONTICS
the experiment. Radiographs were taken before and after each pulp-capping procedure. Molars and premolars were selected because of their larger pulpal chambers. Maxillary right first molars and premolars were used as control teeth with calcium hydroxide. Tricalcium phosphate ceramic powder* was used in the remaining molars and premolars. All animals were approximately four years of age and were close to the same weight. The anesthetics used were phencyclidine hydrochloride intramuscularly and pentobarbital intravenously. Atropine was administered intramuscularly to control salivation. The teeth were isolated with a rubber dam. They were disinfected with povidone-iodine solution for five minutes. The occlusal portion of the tooth was opened with a high-speed no. 4 round bur. The same bur was used to remove the roof of the pulpal chamber. The vital pulpal tissue in the chamber was removed with a small-spoon excavator to minimize injury to the remaining tissue in the root canals. After the pulpotomy was completed, hemorrhage was controlled with a sterile cotton pellet. Pressure was applied until a blood clot formed on the canal tissue stumps. The excess blood and the clot were rinsed from the chamber with physiological saline solution. A paste of tricalcium phosphate ceramic powder in physiological saline solution was applied to 22 teeth as the experimental pulp-capping material. A paste of calcium hydroxide powder in physiological saline solution was applied to the pulp stumps of seven teeth as the control material. The pulp-capping materials were placed over the blood clot of the pulpal tissue of the canals. Because of the evaporation of the saline solution, it was difficult to place the same amount of paste over each site of exposure. After the calcium hydroxide or tri96
calcium phosphate ceramic paste was placed as the pulp-capping agent, a mix of fast-setting zinc oxide and eugenol was used to form a protective base before placement of the final amalgam restoration. The zinc oxide and eugenol base was placed with care to avoid pushing the pulp-capping materials into the tissue of the canal. Radiographs were taken preoperatively, postoperatively, and immediately postmortem. The monkeys were anesthetized with phencyclidine hydrochloride and pentobarbital; they were killed by perfusion with 10% Formalin at 2-, 3-, 5-, 8-, 16-, and 24-week periods. After death, the mandible and maxilla were removed and stripped of soft tissue; they were sectioned so that a tooth remained in each section. The block sections were fixed in 10% Formalin for two weeks and then demineralized in 5% formic acid. The specimens then were embedded in paraffin and cut serially at 6/xm to 10/zm. Each section was cut longitudinally in a mesiodistal plane. Every fifth section was stained routinely with hematoxylin and eosin and examined microscopically. In areas that were important to the study, every section was stained. The results were evaluated in the following manner: The pulps were examined for low, moderate, or severe inflammation, and for vascularization. Connective tissue repair of the pulp at the site of exposure; calcification of the site of exposure; and the conditions of the odontoblastic and predentinaI layers and the periapical tissue were evaluated. Results
No gingival disease was observed before the initiation of the operative procedures or just before killing. The radiographs that were taken before the pulp-capping procedures, immediately after the procedures, and at the
VOL. 1, NO. 3, MARCH 1975
time of killing showed no periapical changes. Because of the small pulpal canals, the presence or absence of a calcified bridge could not be discerned radiographically, either with the ceramic form of tricalcium phosphate or calcium hydroxide. The following results are histological evidence of the specimens. 9 Two-week postoperative experimental results. Three specimens were examined (Fig 1, top). The specimens showed evidence of a fibrous matrix forming at the coronal end of the root canal. There was no evidence of a calcified bridge. There was a characteristic compartmentalization of this matrix. These compartments appeared to be areas of connective tissue surrounding the tricalcium phosphate ceramic particles; there was evidence of a generous blood supply. The compartments gave the appearance of a basket-weave; the connective tissue and tricalcium phosphate ceramic particles were interspersed throughout the coronal portion of the canal. The index of inflammation was low. The odontoblasts appeared viable and undisturbed while the predentinal layer was thickened. The periapical tissues s h o w e d n o evidence of inflammation. 9 Two-week postoperative control. Two specimens were examined (Fig 1, bottom). One specimen showed complete necrosis throughout the pulpal chamber; the canals had moderate periapical inflammation. The other specimen showed evidence of a fibrous matrix beginning to develop at the coronal end of the root canals. A low index of inflammation was evident in the coronal portion of the pulpal canals. There was no inflammation in the periapical tissues. The odontoblasts appeared undisturbed with no thickening of the predentinal layer. 9 Three-week postoperative experimental results. Three specimens were examined (Fig 2, left). Each speci-
JOURNAL OF ENDODONTICS [ VOL. 1, NO. 3, MARCH 1975
Fig 1--Top: Two-week postoperative experimental results (FM, fibrous matrix; TCPC, tricalcium phosphate compartments; BS, blood supply). Dark areas are tricalcium phosphate ceramic particles. Bottom: Two-week postoperative control (D, dentin; O, odontobIasts (orig mag XIO0)).
Fig 3--Top left: Five-week postoperative experimental results (TCPC, tricalcium phosphate compartments; BS, blood supply; CM, calci/ied matrix; O, odontoblasts). Bottom: Five-week postoperative experimental results (TP, thickened predentin). Top right: Five-week postoperative control. Void areas are seen in pulpal tissue adjacent to calcified bridge and thickened predentin (orig mag XIO0). men showed similar results when compared to the two-week specimen except for the evidence of a more developed matrix forming over the exposed pulp. A low index of inflammation was observed in both the coronal and apical portions of the pulp; there was no inflammation in the periapical tissues. There was evidence of a thickened predentinal layer continuous with the fibrous matrix. Vascular supply was evident throughout the pulpal tissues. The odontoblasts were undisturbed.
9 Three-week postoperative control. Fig 2--Left: Three-week postoperative experimental results (FM, fibrous matrix; TCPC, tricaIcium phosphate compartments; BS, blood supply). Right: Three-week postoperative control (Abs, abscess; V, vacuoles seen throughout odontoblastic layer (orig mag XIO0)).
The specimen that was examined (Fig 2, right) showed a fibrous matrix forming at the coronal end of the root canals. There was a large void area lined with connective tissue that 97
JOURNAT. OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
Fig 5--Le/t: Sixteen-week postoperative experimental results. Dark granules are remaining tricalcium phosphate particles (TCPC, tricalcium phosphate compartments; CM, calcified matrix; TP, thickened predentin; BS, blood supply). Right: Sixteen-week postoperative control (CB, calcified bridge; D, dentin; O, odontoblasts (orig mag X250)).
Fig 4--Top: Eight-week postoperative experimental results (TCPC, tricalcium phosphate compartments; CM, calcified matrix; V, viable cells in matrix; O, odontoblasts; BS, blood supply). Bottom: Eight-week postoperative control (CB, calcified bridge; D, dentin; R, reticular atrophy; Abs, abscess (orig mag XIO0)).
was apical to the forming matrix. There were vacuoles throughout the odontoblastic layer and moderate inflammation adjacent to the forming matrix. The predentinal layer was thickened. There was a low index of inflammation in the periapical tissues.
9 Five-week postoperative experimental results. In the four specimens that were examined (Fig 3, top left, bottom), there was evidence of a cal98
cified matrix forming at the coronal end of the root canals. The compartments were well-defined; the walls surrounding the remaining tricalcium phosphate ceramic were thicker than was evident in the three-week study. It appeared that the tricalcium'phosphate ceramic particles were being phagocytized or were being dissolved within the matrix compartments. All four specimens showed viable odontoblasts with a thickened predentinal layer continuous with the calcified matrix. Some areas of the predentinal layer contained cells that appeared to be entrapped odontoblasts. The thickened predentinal layer and calcified matrix formed a continuous cap over the exposed pulp. Histological serial sections showed that the calcified matrix Was a complete layer from one side of the canal to the other. Blood vessels were evident throughout the compartmentalized matrix. The periapical tissues and the apical pulpal tissues were free of inflammation.
9 Five-week
postoperative
control.
The specimen that was examined (Fig 3, top right) showed a well-developed bridge. Histological serial examination showed that the bridge was not complete from wall to wall of the canal.
The predentinal layer was thickened and continuous with the calcified bridge. There were few odontoblasts adjacent to the coronal portion of the bridge. There was evidence of a void area beginning adjacent to the thickened predentinal layer and inferior to the calcified bridge. Apical odontoblasts a~apeared to be viable with a small amount of predentinal thickening. There were few blood vessels. The periapical tissue and the apical pulpal tissue showed a low index of inflammation.
9 Eight-week postoperative experimental results. Three specimens were examined (Fig 4, top). The individual compartments showed more calcification than the five-week specimens did; there was less evidence of particles of tricalcium phosphate ceramic. Viable cells, perhaps fibroblasts or ostoidproducing cells, were evident within the areas of the matrix. The odontoblastic layer was viable and undisturbed from the coronal matrix to the apex. The predentinal layer was thickened only at the coronal portion
JOURNAL OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
where it united with the calcifying matrix. The pulpal tissues showed no inflammation; they had an abundant blood supply. Histological serial sections showed that the calcified matrix was complete from one side of t h e canal to the other in two specimens. In the other specimen, it was almost complete. The periapical tissues showed no inflammation.
9 Eight-week postoperative control. The specimen that was examined (Fig 4, bottom) showed a calcified bridge. Serial sections showed that the calcified bridge was not complete from one side of the canal to the other side; there was soft tissue in some sections. The odontoblastic layer showed areas of vacuolization from the calcified bridge to the apex. There was no evidence of thickening of the predentinal layer below the bridge. Reticular atrophy with areas of scattered necrosis was observed in the center of the pulpal tissue. An abscess appeared to be forming under an area of the bridge in several sections. There were few blood vessels. The pulpal and periapical tissues had a low index of inflammation.
9 Sixteen-week postoperative experimental results. Of the three specimens that were examined (Fig 5, left), one specimen showed complete necrosis throughout the chamber and canal. The periapical tissue had a low index of inflammation. The other two specimens Fig 5, left showed the characteristic compartmentalization of the calcified matrix. Most of the particles of tricalcium phosphate ceramic had resorbed within the compartments; this allowed for thicker and more calcified walls. The predentinal layer was thickened and contiguous with the calcifying matrix. Serial sections showed that the calcified matrix formed a complete wall-to-wall bridge of the canals. Viable cells were evident within the calcifying matrix. The pulpal tissues and periapical tissues showed no inflammation. The odontoblasts
Fig 6--Twenty-/our week postoperative experimental results. Top le/t: CM, calcified matrix; CB, calci/ied bridge; D, dentin (orig mag XIO0). Bottom: O, odontoblasts; TP, thickened predentin (orig mag X250). Top right: (orig mag X250). were not well defined. Blood vessels were throughout the pulpal tissue as well as within the compartmentalized matrix.
9 Sixteen-week postoperative control. One specimen was examined (Fig 5, right). Serial sections showed that a calcified bridge was formed that was completely wall to wall of the canal. The pulpal and periapical tissues showed no evidence of inflammation. The dentinal walls of the pulpal canals were irregular. The predentinal layer was thickened at the coronal end of the pulpal canals while the odontoblasts were undisturbed. Blood vessels were observed throughout the pulpal tissue.
9 Twenty-/our week postoperative experimental results. Three specimens were examined (Fig 6); they showed essentially the same results. The most coronal portion of the pulpal cap
showed very little evidence of remaining tricalcium phosphate ceramic. The walls of the calcified matrix were thicker than the walls of the 16-week specimen; thus, the individual compartments were smaller. Cells were evident within the walls of the calcified matrix. There were blood vessels throughout the calcified matrix and compartments. Directly under the calcified matrix compartments, there was an area of scattered solid calcifications mixed with blood vessels. Apically, there was an area of complete calcification. Serial sections showed a complete wall-to-wall bridge of the canals. The bridge showed evidence of a few cells. U n d e r the calcified bridge, there was an area of thickened predentin that was contiguous with the thickened predentinal area from the sides of the canal walls. The thickened portion of predentin was corn-
99
JOURNAL OF ENDODONTICS [ VOL. 1, NO. 3, MARCH 1975
plete throughout from one side to the other side of the canals. Directly under the predentinal layer, there was a continuous line of odontoblasts in direct apposition to the predentinal layer adjacent to the calcified bridge. The odontoblasts were viable and functional as shown by the thickness of predentin. A few small calcified bodies were in apposition to the coronal odontoblasts. Both the pulpal and periapical tissues were vascular; there was no evidence of inflammation.
9 Twenty-four week postoperative control. The specimen that was examined (Fig 7) showed complete necrosis of the pulpal chamber and the pulpal canal. There was evidence of moderate inflammation of the periapical tissue and possible formation of an abscess in the periapical tissues.
Discussion The results of the study showed that the ceramic form of tricalcium phosphate stimulates the formation of a calcified bridge and that it maintains
Fig 7--Twenty-four week postoperative control (I), dentin; NCP, necrotic pulpal canal (orig mag X58)).
100
a noninflammatory, viable pulp. Twenty-one of 22 pulps treated with tricalcium phosphate ceramic showed favorable results histologically. Three reasons are possibly responsible for this result. The first reason is the development and close apposition of a blood supply to the calcified bridge. The second reason is a possible anti-inflammatory capability in this material. The third reason may be the close chemical resemblance of tricalcium phosphate ceramic to bone or dentin or both. The breakdown products of the tricalcium phosphate may possibly be a contributory factor toward development of the calcified bridge. Both Nyborg '~ and Clark I o showed that there was an area of necrosis and lysed red blood cells adjacent to the calcified bridge when calcium hydroxide was used. Therefore, the calcium hydroxide actually causes the necrosis; this stimulates the pulpal cells to lay down a calcified bridge. However, this bridge usually does not have a vascular supply. This study confirmed their findings. It is likely that some of the zinc oxide and eugenol cement was unavoidably pushed through the layers of calcium hydroxide and tricalcium phosphate ceramic paste; this could have affected the results. Only 1 of 22 pulps reacted unfavorably histologically when treated with tricalcium phosphate ceramic. However, after the same procedures with calcium hydroxide, two teeth had completely necrotic pulps and one tooth had a partial bridge with an underlying pulpal abscess and reticular atrophy. Thus, calcium hydroxide histologically failed three of seven times as a direct pulp-capping agent. In the other four teeth, the pulps remained viable; two formed a fibrous protective matrix, one formed a partial bridge, and one formed a completely calcified bridge.
This study was conducted with the use of healthy teeth of adult monkeys. Further studies are needed using teeth whose pulps have been exposed because of caries or trauma. Further studies also are needed to find a cement-type base material that is potentially less toxic to pulpal tissue than zinc oxide and eugenol. Polycarboxylate cement holds promise as a cement-type base material. 11 Tricalcium phosphate ceramic should be studied for periods of longer time to evaluate the healed pulp's reaction to the test of time and also its response to new insult. There is also the question: If endodontic therapy is ultimately necessary, would there be interfering aberrant calcifications that would complicate treatment? Tricalcium phosphate ceramic appears to be an excellent pulp-capping material; it is inexpensive and easily applied. Clinical studies of human teeth are now felt to be desirable to substantiate the findings of the study.
Summary The purpose of the study was to evaluate a resorbable form of tricalcium phosphate ceramic as a direct pulp-capping agent in the permanent teeth of monkeys. Tricalcium phosphate ceramic powder was mixed with physiological saline solution and was used as a direct pulpal cap in 22 teeth. As a control, the pulps of seven teeth were capped with calcium hydroxide powder mixed with physiological saline solution. The monkeys were killed at 2-, 3-, 5-, 8-, 16-, and 24-week intervals. One of the 22 teeth whose pulp was capped with tricalcium phosphate ceramic showed a necrotic pulp. The remaining teeth showed various levels of formation of matrix, vascularization, and compartmentalization. The 24week specimens showed contiguous calcified bridges spanning the sites of exposure.
JOURNAL OF ENDODONTICS I VOL. 1, NO. 3, MARCH 1975
Of the seven teeth whose pulps were capped with calcium hydroxide, two showed completely necrotic pulps, and one showed a partially calcified bridge with a pulpal abscess and reticular atrophy. In the other four teeth, the pulps remained viable; two formed a fibrous protective matrix, one formed a partial bridge, and one formed a completely calcified bridge. Conclusions
A contiguous calcified bridge can be expected to form over a pulpal exposure when it is capped with tricalcium phosphate ceramic. The pulpal tissue was in close apposition to the calcified bridge and showed minimal inflammation; the pulpal tissue was well vascularized. An odontoblastic layer lined the pulpal surface of the calcified bridge. A thickened layer of predentin lined the walls of the canal and was contiguous with the calcified bridge. Tricalcium phosphate ceramic should be used experimentally as a direct pulp-capping agent in studies on human teeth.
*Synthos: A high purity, specially prepared and processed form of tricalcium phosphate. MITER, Inc., 633 High St, Worthington, Ohio 43085. The opinions and assertions herein are those of the authors and are not to be construed as official or as reflecting the views of the Navy Department or the naval service at large. Dr. Heller is an endodontist in private practice; Dr. Koenigs is an active duty endodontist (DC) USN; Dr. Brilliant is director of graduate endodontics, Ohio State University School of Dentistry; Dr. Melfi is chairman of biological studies, Ohio State University School of Dentistry; and Mr. Driskell is an adjunct professor, Ohio State University School of Dentistry. Requests for reprints should be directed to Dr. Heller, 6586 Worthington-Galena Road, Worthington, Ohio 43085.
References
1. Stanley, H.R. How much could we learn? Justification for establishing a registry for pulpal pathology. Oral Surg 29:265 Feb 1970.
2. Berman, D.S., and Massler, M. Experimental pulpotomies in rat molars. J Dent Res 37:229 April 1958. 3. Glass, R.L., and Zander, H.A. Pulpal healing. J Dent Res 28:97 April 1949. 4. Doyle, W.A.; McDonald, R.E.; and Mitchell, D.F. Formocresol versus calcium hydroxide in pulpotomy. J Dent Child 29:86 April-June 1962. 5. Nyborg, H. Capping of the pulp. The processes involved and their outcome. A report of the follow-ups of a clinical series. Odontol Tskr 66:296, 1958. 6. Langeland, K. Capping exposed pulpal tissue. Clin Dent 2:1 Jan-Feb 1974. 7. Bhaskar, S.N., and others. Biodegradable ceramic implants in bone. Electron and light microscopic analysis. Oral Surg 32:336 Aug 1971. 8. Driskell, T.D., and others. The significance of resorbable bioceramics in the repair of bone defects. Proc 26 Annual Conference on Engineering in Medicine and Biology. 1973. 9. Nyborg, H. Healing processes in the pulp on capping. Acta Odontol Scand 13:9 (Suppl. 16) 1955. 10. Clarke, N.G. The morphology of the reparative dentine bridge. Oral Surg 29:746 May 1970. 11. Spangberg, L.; Rodrigures, H.; and Langeland, K. Biologic effects of dental materials. Oral Surg 37:113 Jan 1974.
101